The present invention relates to a laser beam scanner and in particular to a laser beam scanner apparatus used in a laser beam printer or a character reader employing electrophotography.
As disclosed in the U.S. Pat. No. 4,384,297, in a laser beam printer, a laser beam emitted from a semiconductor laser oscillator is shaped by a beam shaping lens, deflected by a deflector, and focused to form a beam spot on a recording medium by a focusing lens. The deflector moves the beam spot in a direction perpendicular to the running direction of the recoding medium and repetitively forms scanning lines. A driving circuit controls the semiconductor laser oscillator on the basis of a video signal to form an image on the recording medium.
When a photosensitive recording medium for electrophotography is used, the recording medium is uniformly electrified by an electrifier and then exposed by scanning of the laser beam to form an electric latent image. This electric latent image is subjected to toner development. The toner image is reproduced and fixed on a recording sheet.
As disclosed in the U.S. Pat. No. 3,787,107, in a character reader, a laser beam emitted from a laser oscillator is deflected by a deflector to scan the document surface. The reflected light is converted into a video signal by a transducer.
Detailed examination of the reproduced image or video signal resulting from such a conventional laser beam printer or character reader indicates that the image is not faithfully drawn or the image has not been faithfully subjected to photo electro conversion. In image recording, fine black lines (hereafter referred to as "black whiskers") appear in the white background or fine white lines (hereafter referred to as "white whiskers") appear in the black background. Additionally, thinner character or thicker character phenomenon may be found. In image reading, the image density on the scanning line does not accurately correspond to the magnitude of the video signal. In addition, these phenomena occur periodically in relation to the deflection angle of the laser beam, i.e., the scanning position of the laser beam spot.